LED Colors and Vision (pics)

[UnknownVT]

Re: LED Colors and Vision

Good input PhotonBoy, many thanks.

Again I'm not any authority - but I think/believe that blue light is more easily scattered, being a shorter wavelength - plus our eyes have more difficulty focussing blue.

So White light - which has a relatively large component of Blue (especially in comparison to the typical urban environment at night) will tend to Glare/dazzle...

Witness the new HID car headlights - I don't think it's just the brightness but the much higher Blue component in the light - also it has been almost "universal" that yellow/amber is used in fog lights, so as not to cause glare/dazzle when reflected back by white fog.

I know it's obvious but we see by reflected light - and at night
(1) our eyes are adapted/used to seeing by light that tends to lack Blue wavelengths - so our eyes' blue receptors are probably at their most sensitive, since there is a lack of Blue.
So any introduction of higher intensity of Blue will tend to glare/dazzle the eyes - since the eyes are all of a sudden flooded/saturated with blue from its most sensitive state.

(2) White surfaces like paper - tends to reflect all the wavelengths more or less equally - so if trying to read using white illumination from dark adapted eyes - the reflected illumination definitely glares/dazzles in my experience. Again some evidence is the use of non-glare yellow paper.

(3) Yellow and black - I read years ago tends to give the highest (color) contrast so even the use outdoors is very suitable, since yellow/amber tends to give higher contrast than say blue or green - and white. At least that's what I have experienced. Yellow somtimes seems to enhance definition and contrast (for me).

But my limited experience may well be a case of "apples and oranges" - as the yellow/amber LED lights I have are relatively dim in comparison to my white LED lights.

But despite of that, often I seem to be able to see better with the yellow than with the white - I think it's a contrast thing. However for color rendition/recognition White is definitely prefereable/superior.

However for eyes to recover their dark adaption (and this is NOT true scotopic night (rods only) vision) I seem to do a lot better with yellow.

I existed with a single yellow Photon only, for years.
But have recently added a nice CMG Ultra-G (white) as my EDC.

Often when I use Ultra-G to illuminate reading (on white paper) I wish I had used the yellow Photon instead.

 

[Wingerr]

Re: LED Colors and Vision

I was curious about how those red LED pictures turned out,
and tried it on my Minolta G400, below:

white LEDs from Inova 24-7

red LEDs from Inova 24-7

The original pictures doesn't seem to have that pronounced a difference in focus; so it may be something to do with the camera's focusing mechanism rather than an inherent characteristic of using red light. Regular autofocus mode used, and fixed daylight color balance.
I cropped the pictures to keep the width down for the benefit of the resolution challenged, and the photobucket's downsized shot looks somewhat softer than the original.
Original shots in red and white -

(probably need to copy link into browser since hotlinking to the new imagestation doesn't fly anymore)

 

[UnknownVT]

Re: LED Colors and Vision

[ QUOTE ]
Wingerr said:
I was curious about how those red LED pictures turned out,
and tried it on my Minolta G400, below:
The original pictures doesn't seem to have that pronounced a difference in focus; so it may be something to do with the camera's focusing mechanism rather than an inherent characteristic of using red light. Regular autofocus mode used, and fixed daylight color balance.

[/ QUOTE ]

My apologies for the very late reply - I haven't been monitoring this thread.

There is obviously some difficulties in your red LED photo in that finer details cannot be resolved/seen properly - eg: both instances of the (white on black) word "adhesive" at the bottom of the clue tubes.

I do realize that different cameras may have different behaviors - but in my previous post above -

QUOTE:
Red Color photo - this is no better than the previous version in the opening post - if not a tad worse visually - but as we can see it is not a focussing or camera/subject movement problem since the converted to B&W/greyscale image shows very sharp details....
it HAS to be the color red itself causing imaging difficulties.
UNQUOTE

Also the B&W shot taken under the RED LED turned out to be a very well focussed and sharp photo - showing that it is not a focussing problem (at least not on my camera).

 

[Wingerr]

Re: LED Colors and Vision

[ QUOTE ]
UnknownVT said:
There is obviously some difficulties in your red LED photo in that finer details cannot be resolved/seen properly - eg: both instances of the (white on black) word "adhesive" at the bottom of the clue tubes.


[/ QUOTE ]

I think that was primarily due just to underexposure; if I lit it up the same as the lettering above, it should be easily readable.
If your camera has manual focus, maybe you can see if bypassing the autofocus and exposure changes things.

 

[UnknownVT]

Re: LED Colors and Vision

[ QUOTE ]
Wingerr said:
If your camera has manual focus, maybe you can see if bypassing the autofocus and exposure changes things.

[/ QUOTE ]

The shot taken under the same conditions under the RED led light - simply changing the camera settings to B&W (ie: same auto focus, same auto exposure) yielded shots (more than one) that were well focussed and sharp, so it was not a focussing problem.

Whereas the numerous shots under the same conditions under the RED led light - with only the camera setting on regular color and daylight white balance mode - all came out ill defined - as-is.

Taking the RED led color photos and removing the color - ie: changing the mode to grayscale in my photo editor definitely makes the photos look noticably clearer.

This again shows that the photo may look murky in the red color - but the basic grayscale image is in focus.

 

[Wingerr]

Re: LED Colors and Vision

Maybe the terminology is throwing me off-

This was one of the images from above that was Converted from Color, which I guess is a picture taken in color and then turned into B&W with a photo editor:

Was the second one, Red Converted, done the same way?

Since they appear quite different in clarity, if they were taken the same way, it may just be a matter of trial and error if the camera has problems with the red lighting.

I don't see why red light would inherently cause blurry photos, other than focus and exposure. The type of focusing mechanism used in the camera probably plays a part in this;
I'd suspect the different schemes for focusing differ in their sensitivity to the color of the light-
TTL phase differential detection,
Video signals + external passive,
TTL contrast detection, etc.

Converting pictures to greyscale might also appear to sharpen the pictures if the number of levels are reduced, effectively increasing contrast.
Either way, the second shot looks much sharper than the original shot. I think experimenting with manual focus might give you the best results, rather than relying on the autofocus.

 

[UnknownVT]

Re: LED Colors and Vision

[ QUOTE ]
Wingerr said:
Maybe the terminology is throwing me off-

This was one of the images from above that was Converted from Color, which I guess is a picture taken in color and then turned into B&W with a photo editor:

Was the second one, Red Converted, done the same way?

Since they appear quite different in clarity, if they were taken the same way, it may just be a matter of trial and error if the camera has problems with the red lighting.

I don't see why red light would inherently cause blurry photos, other than focus and exposure.

[/ QUOTE ]


Same conversion -

These are the pairs:

"Red3" - Color Image >> Converted to Grayscale/B&W

"Red4" - Color Image >> Converted to Grayscale/B&W

I agree that the B&W image of "Red3" is less clear than that of the "Red4" - so there is some inconsistency - variation.

However look carefully at B&W of "Red3" - and one can see the map details near the tip of the pen and the pen itself is sharp - showing it is not out of focus.

BUT the main point is to look at the photo Pairs - the colored image verses the Grayscale/B&W image -
the B&W is noticably clearer than the colored, in each respective pair.

So it is a color issue and not a focussing issue - besides my digicam uses a white focussing assist lamp - which was in use in each case, and at the distance it was WAY brighter than the red led illumiation, which probably did NOT contribute much to the focussing.

Why RED should seem murky is a mystery to me as well, as I do a lot of photography and have not come across this as an issue. You might note Quickbeam said he also had problems taking photos under red light.

 

[Wingerr]

Re: LED Colors and Vision

I think the problem is blooming of the red channel in your pictures; basically it's overexposed, and by deleting that information from the picture when desaturating, the details from the other channels are able to come through.

 

[UnknownVT]

Re: LED Colors and Vision

[ QUOTE ]
Wingerr said:
I think the problem is blooming of the red channel in your pictures; basically it's overexposed, and by deleting that information from the picture when desaturating, the details from the other channels are able to come through.

[/ QUOTE ]

Thanks for the suggestion - does sound plausible -

but how do you explain the parts of the colored photos which are clearly UNDERexposed - ie: the edges of the lit portion where the image is fading toward black - still not being sharp.

and why is it that the OVERexposed parts - eg: near the tip of the pen in the colored photo - seem to be better defined?

 

[Wingerr]

Re: LED Colors and Vision

[ QUOTE ]
UnknownVT said:
Thanks for the suggestion - does sound plausible -

but how do you explain the parts of the colored photos which are clearly UNDERexposed - ie: the edges of the lit portion where the image is fading toward black - still not being sharp.

and why is it that the OVERexposed parts - eg: near the tip of the pen in the colored photo - seem to be better defined?

[/ QUOTE ]

It's probably just a combination of focus and exposure issues.
As another test, I took two pictures with another camera, this time a Pentax Optio 33L, using my 24/7 for lighting:


This was using the four white LEDs.



This was using the two red LEDs for lighting-



B&W setting in the camera with red lighting


The sharpness between the two doesn't seem to be anything significant, so I don't think there's anything inherent in red lighting that necessarily causes fuzzy pictures.
You may want to try decreasing the EV setting on your camera to see if it will correct the blooming; I did have to drop the exposure down on the red picture to keep it from getting overexposed, because that's what it was doing when using the autoexposure mode of the camera. Probably balanced for white lighting, and thrown off by the monochromatic red.

 

[UnknownVT]

Re: LED Colors and Vision

[ QUOTE ]
Wingerr said:
The sharpness between the two doesn't seem to be anything significant, so I don't think there's anything inherent in red lighting that necessarily causes fuzzy pictures.

[/ QUOTE ]

I do thank you for continuing with suggestions -
(no disrespect meant - but your latest photos are not the same size/scale and they do not contain enough fine details like on a map to make comparisons truly meaningful)

However I downloaded your originals and took crops of finer detail area from the Red and the B&W under red photo (unfortunately the white LED photo is too underexposed in that same area to be useful)

Perhaps you'd like to comment on these crops yourself
(Note: NO sharpening whatsoever was used - only brightness and contrast to bring out the details)

Red crop -- B&W under Red Crop -- Grayscale/B&W Converted from Red crop

IMHO - the B&W taken under red light (middle photo crop) is considerably sharper and better defined than the either of the other two images -
Also I do think I see better detail of the grayscale/B&W converted image from the red than the original red.....

what do you think?

 

[Double_A]

Re: LED Colors and Vision

Hi-

paul

 

[Wingerr]

Re: LED Colors and Vision

I was using macro mode, which has limited depth of field; the portions you cropped out from the red shot was out toward the edge, so it was just out of focus. I didn't use a tripod, so I just did a quick 'n dirty shot of a magazine for comparision.
I'd compare the text in the central portion, looking for the sharpest area of each picture, since the goal was just to see if the focus was the culprit.


Crops of a different section of the pictures






The way the color picture with white light appears blurrier just underscores that it's a matter of focus. I can redo the shots and pick a specific target, but there, I was just looking for the sharpest point in the picture, and shot it at an angle so as to make sure some point in the shot would be in best focus, despite the limitations in the depth of field. In the case of the color shot with white light, the point of focus is a bit further than the cropped area, because you could see the text is sharp two or three lines up.

On a side note, Imageshack is really nifty the way it sets up clickable thumbnails for the uploads- very nice! /ubbthreads/images/graemlins/smile.gif

 

[UnknownVT]

Re: LED Colors and Vision

[ QUOTE ]
Wingerr said:The way the color picture with white light appears blurrier just underscores that it's a matter of focus. I can redo the shots and pick a specific target, but there, I was just looking for the sharpest point in the picture, and shot it at an angle so as to make sure some point in the shot would be in best focus, despite the limitations in the depth of field. In the case of the color shot with white light, the point of focus is a bit further than the cropped area, because you could see the text is sharp two or three lines up.

[/ QUOTE ]

I do understand and appreciate what you were trying to do - the trouble is that the target is too coarse to show the sort of difference we're trying to look for.

If we go back to my problematic photo - Red4 - pardon the repeat and possible waste of bandwidth - but I want to be explicit -

"Red4" - Color Image >> Converted to Grayscale/B&W

This is the exact SAME photo - ie: same exposure, same focus - because the Grayscale/B&W image is merely the red colored image converted to Grayscale/B&W - NO sharpening was used in either photo.

So we KNOW it is NOT a focussing problem.

The suggestion of an UNDER or OVER- exposure problem again is refuted because of the range of lighting in the photo itself - there are areas which are quite obviously Over from the ideal and others which are clearly UNDER-exposed from the optimum.

Yet it is very obvious (to me) the red colored photo is mush less defined than the exact SAME photo with the color removed.

Your suggestion of RED blooming is one of the best -

But if you look at some of the wording like "Lake City" (toward the top left of the lit area) it is clearly legible in Grayscale/B&W mode - whereas it is dramatically NOT readable (even when I know it's supposed to be "Lake City") in the Red color photo.

What it boils down to is that at least for my particular digicam (a Canon PowerShot S100 Digital ELPH) this is a "Red Colored Issue" (for want of a better term) as the digicam does not exhibit this kind of a problem with the other colors I tried such as white, blue, green, red/green = "Yellow", blue/green = "Cyan".

Although I suspect there is a slight problem with the red/blue = "Magenta", although it is not as obvious.

(Please note I had not explicitly said so - but I have taken numerous photos under the red LED light because I found the first few I did were murky/blurry looking and even with repetition and more care - I still failed to get well defined looking red color photos - that's the reason I went to all the trouble of doing these other experiments/variations to try to fathom why my colored photos are like this under red LED light.

Thanks for your efforts - much appreciated.

So far "Red Blooming" is the best (albeit partial) explanation -
but there are probably other issues
(eg: at the same JPG compression ratios - the red colored photo seems to suffer more degradation than the B&W - when I first processed the crops of your photos, the red colored looked much, much worse - and I had to use a much less compressed JPG to preserve the visible details) -

So as a sort of blanket/informal statement I can say that at least for my sample of one digicam -
it has a "Red light issue" /ubbthreads/images/graemlins/broke.gif

thanks

 

[Wingerr]

Re: LED Colors and Vision

[ QUOTE ]
UnknownVT said:
I do understand and appreciate what you were trying to do - the trouble is that the target is too coarse to show the sort of difference we're trying to look for.


[/ QUOTE ]
From the differences between the two shots in your camera, I didn't think it was really necessary to look for fine differences, only trying to determine if it's possible to get a reasonable shot under red light.
Don't know why your red shots look so bad; could very well be just some peculiarity of the S100, maybe its compression algorithm or something.
Do you have a full size image of that red shot linked somewhere? I assume the one above is a downsized version; looking at it, the red channel looked saturated at 255 over the areas where there was no visible detail.
If you have the full image linked, I'm curious to see what it looks like. Pretty neat how the details were hidden behind the blur of red in your two shots - maybe you've stumbled on a new way to send subliminal images! /ubbthreads/images/graemlins/grin.gif

 

[UnknownVT]

Re: LED Colors and Vision

[ QUOTE ]
Wingerr said:
Don't know why your red shots look so bad; could very well be just some peculiarity of the S100, maybe its compression algorithm or something.
Do you have a full size image of that red shot linked somewhere? I assume the one above is a downsized version; looking at it, the red channel looked saturated at 255 over the areas where there was no visible detail.

[/ QUOTE ]

I think you've hit it.....

The red looks bad - due to a combination of several things -

(1) Post processing by me - I tried to bring out more detail by upping the brightness and contrast - so that bloomed the red channel.

(2) JPG compression - I think this is probably the BIGGEST culprit - jpg seems very sensitive for the RED image - I normally save to a just acceptable jpg70 quality - for the "optimal" smallest size without (much) visible degradation. BUT for this red image jpg70 degrades it a lot - compared to the jpg95 and jpg100 images.

Below are full sized crops withOUT any resize, or post processing - reference saved to jpg95 and all others at my usual jpg70:

RED full-size at jpg95 >>>>> Red full-size at jpg70

Grayscale/B&W converted from Red >>>>> B&W mode taken under Red both saved at jpg70

Many thanks for helping solve this problem.
/ubbthreads/images/graemlins/happy14.gif

PS - thinking of it - I take a lot of images of Swiss Army Knives (SAKs) which have Red handles - and have noticed a lot of jpg artifacts around the Swiss cross logo - I have attempted to save at the higher quality jpg95 and the even jpg100 but it doesn't seem to make a significant enough difference to warrant the much larger file sizes. Most of the recent ones are using a flatbed scanner - so it probably isn't my digicam that's the primary cause of the problem. I'll have to see if this is a particular trait of the editor I'm using, or just JPG itself......

PS2 - I can try to post the full-sized unprocessed Red image somewhere - as there is some visible degradation even from the highest quality jpg100 - but very little visible difference between the jpg95 and jpg100 -
BUT obviously no where near as bad as using the jpg70 as shown

 

[Wingerr]

Re: LED Colors and Vision

Pretty interesting- so JPEG compression might have been playing a role- amazing that you could extract the details back out from the image in those conversions; I would have figured it would have been lost in the first conversion.

Here's a link I came across on Imageshack with some info on the different picture types and compression effects-

On another note:
Imageshack
Doesn't really shed any light on the sensitivity to red, but pretty informative. Didn't know too much about the PNG format, but it looks pretty handy for certain types of pictures.

 

[UnknownVT]

Re: LED Colors and Vision

[ QUOTE ]
Wingerr said:
Pretty interesting- so JPEG compression might have been playing a role- amazing that you could extract the details back out from the image in those conversions; I would have figured it would have been lost in the first conversion.

[/ QUOTE ]

The full-sized Grayscale/B&W converted from the Red Colored photo was done on the original image - then saved at jpg70.
(just to be explicit - it was not the red image saved at jpg70 then converted.)
I always try to work on the original image - and if I have to save an intermediate copy - I save to lossless TIFF and work on that.

Now thinking back - this would explain why despite Red3 looking slightly better than Red4 -
the converted Grayscale of Red4 looked a lot better than the grayscale converted Red3.

The Grayscale converted from Red3 was actually converted from Red3 saved in jpg70 from a previous session - whereas the Grayscale converted from Red4 was done on the (original) image before it was saved, as I was processing both images in the same session.

Good discussion /ubbthreads/images/graemlins/happy14.gif /ubbthreads/images/graemlins/clap.gif - I'm uncovering some nuances I hadn't thought of before.

Thanks.

 

[greg_in_canada]

Re: LED Colors and Vision

Found this (old) thread via the Color Mixing With LEDs thread.

Part of the reason the Red images are less sharp is that
the Bayer matrix in most digital cameras has 2 green
pixels for every 1 red (and every 1 blue). So if you
shoot in monochrome red (or blue) light the camera's
linear resolution is halved. With green you get better
resolution, and with light that contains green and red
(or blue) you have even more resolution.

This is also complicated by the fact that the camera estimates
the color at every pixel location based on the readings
from nearby pixels. Different cameras may be better or worse
converting from monochrome red or blue since the camera manufacturers
likely tweak their algorithms based on full colour photos.
(So some cameras may mess up pure red images more than
others.)

Greg

 

[UnknownVT]

Re: LED Colors and Vision

[ QUOTE ]
greg_in_canada said:
Found this (old) thread via the Color Mixing With LEDs thread.

Part of the reason the Red images are less sharp is that
the Bayer matrix in most digital cameras has 2 green
pixels for every 1 red (and every 1 blue).

[/ QUOTE ]
I thank you for that input.

However the Bayer interpretation by major digicam companies is pretty well known and established.

The problems I was having with the Red images seem to be more to do with the degree of compression used in the JPG format. Red seems to be more sensitive to compression than any other color.

JFYI - I have done lots of test shots with colored (Red, Green & Blue) resolution test panels and although there are some (slight) differences between the colored panels - they're nothing like the (near horrendous) degradation we see in my Red images - that is due to the (higher) JPG compression used. There's quite a bit about it earlier on in this thread.

Thanks,